(a) Field of the Invention
The present invention relates to a means and method for disposing of by-products of coal and coal combustion, and particularly relates to the formation of hardened, environmentally inert and disposable composite granules consisting of coal cleaning refuse and coal combustion wastes.
Substantial amounts of energy are produced by the combustion of coal. As with any energy-generating process, the coal combustion process results in by-products and waste, which must be dealt with.
The general composition of coal, and its by-products and wastes, present serious environmental problems, primarily to the air, streams and ground water. Combustion wastes primarily consist of fly ash which many times contains heavy metals which are highly damaging to the environment in the concentrations contained in fly ash. Concentrations of heavy metals in fly ash are often quite small, but their presence can become highly damaging to the environment because several of the heavy metals will segregate on the surface of the fly ash particles during the combustion and subsequent flue gas cooling.
The problem is exacerbated because of the tremendous volume of coal cleaning and coal combustion wastes generated annually in the United States. It is estimated that there is annually 100 million tons of coal cleaning refuse containing rejected unusable coal produced in the United States. In addition, it is estimated that coal combustion results in the production of 60 million tons of fly ash and 25 million tons (dry basis) of flue gas desulfurization sludge annually. Conventionally, because of the adverse environmental impact of such materials, the rejected coal refuse and combustion wastes are many times simply stockpiled at locations near the coal mining or combustion facilities. Leaching of the heavy metals occurs to the ground, and this contamination eventually enters the nearest open water ways, and ground water. It can then be carried and spread to wide areas. Also, exposure to the elements allows the wind to carry away finer particles which causes dusting of surface vegetation and structures, and contributes to air pollution. Additionally, the coal cleaning refuse may ignite and cause smoldering in the piles of material, which would in turn cause pollutants to enter the atmosphere.
There have been many attempts to deal with this important environmental problem. Some attempts involve trying to recombust the coal cleaning refuse and/or co-combustion wastes, to diminish their quantity, and to reduce the potential impact on the environment. Other methods attempt to mix the coal cleaning refuse and combustion waste with other materials to reduce their environmental impact. None of these methods have proven to be entirely satisfactory from an environmental standpoint.
The present inventors previously developed a method for producing hardened granules made from coal cleaning refuse and coal combustion waste which proved to be durable and able to withstand environmental and chemical forces which generally break down or contribute to the environmental problems associated with coal combustion waste and coal cleaning refuse. That method first ground the coal cleaning refuse and then blended or mixed the ground coal cleaning refuse with coal combustion waste. This blended mixture was then put in a mechanism to form generally spherical granules of the mixture. Water or some other binding liquid was usually required to facilitate the binding. The granules were then sent to a furnace whereby they were combusted and sintered. The carbon content of the coal cleaning refuse and coal combustion waste comprised the combustible portion of the mixture and elevated the granules to sintering temperature. Upon cooling, the sintered mixture fuses together to form a hardened granule which is resistant to environmental factors and chemicals which would try to break the particles down.
A method has been discovered, however, which produces even more durable and harder granules which will further ensure safe environmental disposal of these coal combustion by-products and wastes. This improved method, set forth herein, represents an advance in the art and a solution to the serious environmental problems described above.
It is therefore a principal object of the present invention to solve or improve over the problems and deficiencies in the art.
Another object of the present invention is to provide a hardened, environmentally inert composite granule of coal cleaning refuse and coal combustion waste which stabilizes the constituent elements of those substances and is in a form which is easily handled and disposable.
A further object of the present invention is to provide a means and method as above described which is highly resistant to environmental degradation and chemical attack, and is nonleachable.
These and other objects, features and advantages of the invention will become more apparent with reference to the accompanying specification and claims.